Setting retransmission time of an application client during virtual machine migration

ABSTRACT

A method of setting retransmission time of an application client during virtual machine migration includes predicting migration memory size required by a virtual machine to be migrated based on historical access log of at least one application and memory log of the virtual machine to be migrated; computing available migration bandwidth of a host of the virtual machine to be migrated; computing virtual machine migration time based on the predicted migration memory size required by the virtual machine to be migrated and the available migration bandwidth of the host; and setting retransmission time of the application client based on the virtual machine migration time.

DOMESTIC AND FOREIGN PRIORITY

This application is a continuation application of the legally relatedU.S. Ser. No. 14/487,288 filed Sep. 16, 2014; which claims priority toChinese Patent Application No. 201310450450.6, filed Sep. 27, 2013, andall the benefits accruing therefrom under 35 U.S.C. § 119, the contentsof which in its entirety are herein incorporated by reference.

TECHNICAL FIELD

The present invention relates to virtual machine migration, and moreparticularly, to a method and system of setting retransmission time ofan application client during virtual machine migration.

BACKGROUND

Currently, virtualization technology has been widely used.Virtualization technology provides an approach capable of accommodatinga plurality of Virtual Machines (VMs) on a large server, which reducestotal cost of user and improves reliability and flexibility ofapplications, thereby reducing possibility of providing excessivecomputing resource by user for spike of various workloads. Moreover,virtualization technology helps to isolate important applications, suchthat different applications running on different virtual machines willnot share operation system, thus critical failure caused by anapplication will not affect applications in any other virtual machines.The virtualization technology is an important and fundamental technologyin “cloud computing” technology, and since it has the capabilities ofon-demand configuration and dynamic migration, it becomes a key forrealizing dynamic and scalable extension of cloud computing. In order torealize the high flexibility of the cloud computing to satisfy policiesand requirements of services or management, dynamic migration andaggregation of virtual machines among physical machines need to beperformed frequently, so as to achieve the objectives of reducing energyconsumption, improving resource utilization and lowering managementcosts, etc.

However, virtual machine migration is a highly I/O sensitive process.During the process that the virtual machine is migrated, since theservices or applications thereon are still in operation, this willproduce unexpected influence on application clients of the virtualmachine. For example, during the process of virtual machine migration,an application client of the virtual machine issues a request to thevirtual machine, this will cause a response failure, thus aretransmission request needs to be sent, the criterion of TCP protocolfor controlling whether a data segmented needs to be retransmitted is toset a retransmission timer. A retransmission timer is started when adata segment is sent. If an acknowledgement is received before the timeris timed out, the retransmission time is turned off. If no acknowledgeis received before the timer is timed out, the data segment isretransmitted. During the process of selecting retransmission time, TCPhas to be adaptive. It needs to give a suitable data retransmission timebased on communication condition of Internet at that time. Currently, afrequently used algorithm is a dynamic algorithm that continuouslyadjust time-out time interval. Its operation principle is as follows: avariable Round Trip Time (RTT) is maintained for each connected TCP,which is used to store an estimated value closest to time required for around trip between current and destination end. If no acknowledge isreceived before the timer is timed out, value of RTT is doubled. Asnumber of times of connection failure increases, value of RTT is largerand larger. During the process of virtual machine migration, since valueof RTT is small, number of times of retransmission will increase. If thevirtual machine migration has already been completed, since value of RTTis larger and larger as number of times of retransmission increases,response delay will occur at client.

Thus, when a virtual machine is being migrated, a suitableretransmission time needs to be set for application client, so as torespond to request of the client in time.

SUMMARY

In one embodiment, a method of setting retransmission time of anapplication client during virtual machine migration includes predictingmigration memory size required by a virtual machine to be migrated basedon historical access log of at least one application and memory log ofthe virtual machine to be migrated; computing available migrationbandwidth of a host of the virtual machine to be migrated; computingvirtual machine migration time based on the predicted migration memorysize required by the virtual machine to be migrated and the availablemigration bandwidth of the host; and setting retransmission time of theapplication client based on the virtual machine migration time.

In another embodiment, an apparatus for setting retransmission time ofan application client during virtual machine migration includes amigration memory predicting module configured to predict migrationmemory size required by a virtual machine to be migrated based onhistorical access log of at least one application and memory log of thevirtual machine to be migrated; an available bandwidth computing moduleconfigured to compute available migration bandwidth of a host of thevirtual machine to be migrated; a migration time computing moduleconfigured to compute virtual machine migration time based on thepredicted migration memory size required by the virtual machine to bemigrated and the available migration bandwidth of the host; and aretransmission time setting module configured to set retransmission timeof the application client based on the virtual machine migration time.

In another embodiment, a non-transitory, computer readable storagemedium has instructions stored thereon that, when executed by acomputer, implement a method of setting retransmission time of anapplication client during virtual machine migration. The method includespredicting migration memory size required by a virtual machine to bemigrated based on historical access log of at least one application andmemory log of the virtual machine to be migrated; computing availablemigration bandwidth of a host of the virtual machine to be migrated;computing virtual machine migration time based on the predictedmigration memory size required by the virtual machine to be migrated andthe available migration bandwidth of the host; and settingretransmission time of the application client based on the virtualmachine migration time.

The method and apparatus according to embodiments of the invention arecapable of setting suitable retransmission time, responding to requestof application clients in time, reducing number of times ofretransmission, and lowering overhead of network transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some embodiments of the presentdisclosure in the accompanying drawings, the above and other objects,features and advantages of the present disclosure will become moreapparent, wherein the same reference generally refers to the samecomponents in the embodiments of the present disclosure.

FIG. 1 shows a block diagram of an exemplary computer system/serverwhich is applicable to implement the embodiments of the presentinvention;

FIG. 2 shows a method of setting retransmission time of an applicationclient during virtual machine migration according to an embodiment ofthe invention;

FIG. 3 shows a change curve of request arrival rate of an application ofthe virtual machine to be migrated within a period of time according toan embodiment of the invention;

FIG. 4 shows a change curve of memory allocated by the virtual machineto be migrated to an application within a period of time according to anembodiment of the invention;

FIG. 5 shows an apparatus of setting retransmission time of anapplication client during virtual machine migration according to anembodiment of the invention.

DETAILED DESCRIPTION

Some preferable embodiments will be described in more detail withreference to the accompanying drawings, in which the preferableembodiments of the present disclosure have been illustrated. However,the present disclosure can be implemented in various manners, and thusshould not be construed to be limited to the embodiments disclosedherein. On the contrary, those embodiments are provided for the thoroughand complete understanding of the present disclosure, and completelyconveying the scope of the present disclosure to those skilled in theart.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Referring now to FIG. 1, in which a block diagram of an exemplarycomputer system/server 12 which is applicable to implement theembodiments of the present invention is shown. Computer system/server 12is only illustrative and is not intended to suggest any limitation as tothe scope of use or functionality of embodiments of the inventiondescribed herein.

As shown in FIG. 1, computer system/server 12 is shown in the form of ageneral-purpose computing device. The components of computersystem/server 12 may include, but are not limited to, one or moreprocessors or processing units 16, a system memory 28, and a bus 18 thatcouples various system components including system memory 28 toprocessor 16.

Bus 18 represents one or more of any of several types of bus structures,including a memory bus or memory controller, a peripheral bus, anaccelerated graphics port, and a processor or local bus using any of avariety of bus architectures. By way of example, and not limitation,such architectures include Industry Standard Architecture (ISA) bus,Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, VideoElectronics Standards Association (VESA) local bus, and PeripheralComponent Interconnect (PCI) bus.

Computer system/server 12 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 12, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 28 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 30 and/or cachememory 32. Computer system/server 12 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 34 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 18 by one or more datamedia interfaces. As will be further depicted and described below,memory 28 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 40, having a set (at least one) of program modules 42,may be stored in memory 28 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. Program modules 42 generally carry out the functions and/ormethodologies of embodiments of the invention as described herein.

Computer system/server 12 may also communicate with one or more externaldevices 14 such as a keyboard, a pointing device, a display 24, etc.;one or more devices that enable a user to interact with computersystem/server 12; and/or any devices (e.g., network card, modem, etc.)that enable computer system/server 12 to communicate with one or moreother computing devices. Such communication can occur via Input/Output(I/O) interfaces 22. Still yet, computer system/server 12 cancommunicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 20. As depicted, network adapter 20communicates with the other components of computer system/server 12 viabus 18. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 12. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

Referring now to FIG. 2, in which a method of setting retransmissiontime of an application client during virtual machine migration accordingto an embodiment of the invention is shown, the method comprising: inblock S201, predicting migration memory size required by a virtualmachine to be migrated based on historical access log of at least oneapplication and memory log of the virtual machine to be migrated; inblock S202, computing available migration bandwidth of a host of thevirtual machine to be migrated; in block S203, computing virtual machinemigration time based on the predicted migration memory size required bythe virtual machine to be migrated and the available migration bandwidthof the host; in block S204, setting retransmission time of theapplication client based on the virtual machine migration time.

In block S201, predicting migration memory size required by a virtualmachine to be migrated based on historical access log of at least oneapplication of the virtual machine to be migrated comprises: computingchange in request arrival rate of the at least one application andaverage service time of each request within a period of time based onthe historical access log of the at least one application; collectingstatistics about change in memory size allocated by the virtual machineto be migrated to the at least one application within the period of timebased on the memory log of the virtual machine to be migrated; computinga function relation between the memory size allocated by the virtualmachine to be migrated to the at least one application and the requestarrival rate of the at least one application within the period of timebased on the change in request arrival rate of the at least oneapplication and the change in memory size allocated by the virtualmachine to be migrated to the at least one application within the periodof time; and predicting migration memory size required by the virtualmachine to be migrated based on the function relation.

According to an embodiment of the invention, predicting migration memorysize required by the virtual machine to be migrated based on thefunction relation comprises: predicting migration memory size requiredby the at least one application based on the function relation andrequest arrival rate of the at least one application at migration time;obtaining migration memory size required by the virtual machine to bemigrated by accumulating memory size required by the at least oneapplication.

According to an embodiment of the invention, it is observed that thereis a linear correlation relationship between memory overhead required bya virtual machine to process each request and average service timecorresponding to each request. When a new request arrives, a virtualmachine will allocate certain memory for serving this request andaverage service time required by request of different types ofapplication varies. Generally, the longer the average service timerequired by a request, the larger the memory allocated for that request.For example, for a complex application A and a simple application B,average service time for request of application of type A is 4 s, andaverage service time for request of application of type B is 2 s. Then,memory size allocated by a virtual machine for request of application oftype A is substantially twice of memory size allocated for request ofapplication of type B. A function relation between memory size allocatedby a virtual machine for an application at any time and average servicetime requested for that application is as follows:S=a*v*Ts+b  (1)

Wherein, S is memory size allocated by a virtual machine for anapplication at any time, a is a proportional coefficient, V is requestarrival rate of that application within a period of time, Ts is averageservice time requested for that application, and b is a correctiveparameter.

According to an embodiment of the invention, a hypervisor may acquire,from a virtual machine to be migrated, historical access log of anapplication of the virtual machine to be migrated, and compute requestarrival rate v of an application within a period of time and averageservice time Ts of each request. Within historical access log of anapplication, operation such as reception, processing of a request andthe like are recorded in time order. According to an embodiment of theinvention, a typical historical access log of an application is asfollows:

Time tag event t0 receive a request from ip0 t1 receive a request fromip1 t2 handle request from ip0 t3 receive a request from ip2 t4 handlerequest from ip1 t5 send reply to ip0 . . . . . . tn_1 handle requestfrom ip2 tn_2 send reply to ip1 tn_3 send reply to ip2

According to the above historical access log, request arrival rate ofthe application within time period t0-t3 may be computed as: v=3/(t3-t0)

Average service time of request of that application is computed as:Ts=(Ts_1+Ts_2+Ts_3)/3.

Wherein, at time t0, service time of request of that applicationreceived from IP address ip0 is: Ts_1=t5−t0.

At time t1, service time of request of that application received from IPaddress ip1 is: Ts_2=tn_2−t1.

At time t3, service time of request of that application received from IPaddress ip2 is: Ts_3=tn_3−t3.

According to an embodiment of the invention, a hypervisor may acquire,from a virtual machine to be migrated, memory log of the virtual machineto be migrated, and may acquire memory size allocated by the virtualmachine to an application at any time based on memory log of the virtualmachine to be migrated. Thus, the proportional coefficient a andcorrective parameter b in equation (1) may be computed according tohistorical data.

FIG. 3 shows a change curve of request arrival rate of an application ofa virtual machine to be migrated within a period of time according to anembodiment of the invention. As shown, horizontal coordinate is time,vertical coordinate is request arrival rate of an application. FIG. 4shows a change curve of memory allocated by a virtual machine to bemigrated to an application within a period of time according to anembodiment of the invention. For example, two coordinate points A, Bcorresponding to two time points are selected in FIG. 3, and twocoordinate points C, D corresponding to the same time points areselected in FIG. 4. At time point of 10 hours, request arrival rate is10/s and memory size allocated by the virtual machine to be migrated tothat application is 2 GB. At time point of 20 hours, request arrivalrate is 20/s and memory size allocated by the virtual machine to bemigrated to that application is 4 GB. Assume that average service timeof request of that application is 2 s, values of the above coordinatepoints are substituted into equation (1),2=a*10*2+b  (2)4=a*20*2+b  (3)

It is solved that a=0.1, b=0, thus equation (1) directed to thatapplication is transformed into:S=0.2*v  (4)

At current time at which the virtual machine to be migrated is to bemigrated, number of requests of the application being served by thevirtual machine to be migrated is queried, request arrival rate of theapplication at current time is acquired, and migration memory sizerequired by the application is computed according to equation (4).

In case that there are a plurality of applications, a function relationbetween memory size allocated by the virtual machine to be migrated tothe plurality of applications and request arrival rate corresponding tothe plurality of applications within the period of time is acquired oneby one by the method according to embodiments of the invention, andmigration memory size required by the plurality of applications arepredicted based on each function relation and request arrival rate atmigration time, then, memory size required by the plurality ofapplications are accumulated to obtain migration memory size required bythe virtual machine to be migrated.

In block S202, computing available migration bandwidth of a host of thevirtual machine to be migrated. According to an embodiment of theinvention, in case that there are a plurality of virtual machinesrequesting bandwidth from the host, if bandwidth of the host is greaterthan or equal to bandwidth requested by the plurality of virtualmachines, then available migration bandwidth of the host of the virtualmachine to be migrated is

${W_{A} = {W_{S} - {\sum\limits_{i = 1}^{j}\; W_{i}}}},$wherein W_(s) is bandwidth of the host, W_(i), (i=1 . . . j, j≥1) isbandwidth requested by other virtual machines except the virtual machineto be migrated. For example, there are two virtual machines A and B on ahost whose bandwidth is 1 Gbps. Bandwidth requested by virtual machine Ais 200 Mbps and bandwidth requested by virtual machine B is 300 Mbps. Ifvirtual machine A is to be migrated, available migration bandwidth ofhost of the virtual machine to be migrated is W_(A)=1 Gbps−300 Mbps=700Mbps. According to another embodiment of the invention, in case thatthere are a plurality of virtual machines requesting bandwidth from ahost, if bandwidth of the host is smaller than bandwidth requested bythe plurality of virtual machines, then available migration bandwidth ofthe host of the virtual machine to be migrated is calculated based onweight of the virtual machine to be migrated. The available migrationbandwidth of the host of the virtual machine to be migrated is

${W_{A} = {\frac{P_{j}}{\sum\limits_{i = 1}^{n}\; P_{i}}W_{S}}},$jϵ(1 . . . n), wherein P_(j) is weight of the virtual machine to bemigrated,

$\sum\limits_{i = 1}^{n}\; P_{i}$is sum of weight of all virtual machines. For example, there are twovirtual machines A and B on a host whose bandwidth is 1 Gbps, bandwidthrequested by virtual machine A is 800 Mbps, weight is 5, and bandwidthrequested by virtual machine B is 500 Mbps, weight is 3. If virtualmachine A is to be migrated, then migration bandwidth is

$W_{A} = {{\frac{5}{5 + 3}*1\mspace{20mu}{Gbps}} = {0.625\mspace{14mu}{{Gbps}.}}}$

In block S203, computing virtual machine migration time based on thepredicted migration memory size required by the virtual machine to bemigrated and the available migration bandwidth, that is, virtual machinemigration time is

${T = \frac{M}{W_{A}}},$wherein M is migration memory size of the virtual machine, W_(A) isavailable migration bandwidth of the host.

In block S204, setting retransmission time of the application clientbased on the virtual machine migration time. In particularly, before avirtual machine is migrated, a hypervisor predicts migration time of thevirtual machine and sets retransmission time of the application clientto be slightly larger than migration time of the virtual machine so asto obtain a relatively accurate retransmission time. According to theretransmission time, a time instruction that a connection may beestablished is issued to the client, and the application client, uponreceiving the instruction, sends a request to the migrated virtualmachines according to the time set in the instruction.

The method of setting retransmission time of an application clientduring virtual machine migration according to embodiments of theinvention has avoided setting Round Trip Time (RTT) as retransmissiontime as in conventional TCP protocol, prevents problems such as increasein number of times of retransmission and response delay of applicationclient etc, rather, it takes into account factors influencing migrationtime of a virtual machine, set retransmission time by using predictedmigration time of the virtual machine so as to set suitableretransmission time, and responds to request of an application client intime.

Based on a same inventive conception, the invention also provides anapparatus of setting retransmission time of an application client duringvirtual machine migration. FIG. 5 shows an apparatus 500 of settingretransmission time of an application client during virtual machinemigration according to an embodiment of the invention, comprising: amigration memory predicting module 501 configured to predict migrationmemory size required by a virtual machine to be migrated based onhistorical access log of at least one application and memory log of thevirtual machine to be migrated; an available bandwidth computing module502 configured to compute available migration bandwidth of a host of thevirtual machine to be migrated; a migration time computing module 503configured to compute virtual machine migration time based on thepredicted migration memory size required by the virtual machine to bemigrated and the available migration bandwidth of the host; aretransmission time setting module 504 configured to set retransmissiontime of the application client based on the virtual machine migrationtime.

According to an embodiment of the invention, wherein the migrationmemory predicting module 501 is further configured to: compute change inrequest arrival rate of the at least one application and average servicetime of each request within a period of time based on the historicalaccess log of the at least one application; collect statistics aboutchange in memory size allocated by the virtual machine to be migrated tothe at least one application within the period of time based on thememory log of the virtual machine to be migrated; compute a functionrelation between the memory size allocated by the virtual machine to bemigrated to the at least one application and the request arrival rate ofthe at least one application within the period of time based on thechange in request arrival rate of the at least one application and thechange in memory size allocated by the virtual machine to be migrated tothe at least one application within the period of time; and predictmigration memory size required by the virtual machine to be migratedbased on the function relation.

According to an embodiment of the invention, wherein the migrationmemory predicting module 501 is further configured to: predict migrationmemory size required by the at least one application based on thefunction relation and request arrival rate of the at least oneapplication at migration time; obtain migration memory size required bythe virtual machine to be migrated by accumulating memory size requiredby the at least one application.

According to an embodiment of the invention, wherein the availablebandwidth computing module 502 is configured to: in case that there area plurality of virtual machines requesting bandwidth from the host, ifbandwidth of the host is greater than or equal to bandwidth requested bythe plurality of virtual machines, then available migration bandwidth ofthe host of the virtual machine to be migrated is

${W_{A} = {W_{S} - {\sum\limits_{i = 1}^{j}\; W_{i}}}},$wherein W_(s) is bandwidth of the host, W_(i), (i=1 . . . j, j≥1) isbandwidth requested by other virtual machines except the virtual machineto be migrated.

According to an embodiment of the invention, wherein the availablebandwidth computing module 502 is configured to: in case that there area plurality of virtual machines requesting bandwidth from the host, ifbandwidth of the host is smaller than bandwidth requested by theplurality of virtual machines, then compute available migrationbandwidth of the host of the virtual machine to be migrated based onweight of the virtual machine to be migrated.

According to an embodiment of the invention, wherein the retransmissiontime setting module 504 is further configured to set retransmission timeof the application client to be slightly larger than migration time ofthe virtual machine.

For detailed implementation of each of the above modules, reference maybe made to description of the method of setting retransmission time ofan application client during virtual machine migration according toembodiments of the invention, which will be omitted here for brevity.

The method and apparatus of setting retransmission time of anapplication client during virtual machine migration according toembodiments of the invention may be installed in a hypervisor as aplug-in of an application.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method of setting retransmission time of anapplication client during virtual machine migration, the methodcomprising: predicting, with a processing device, migration memory sizerequired by a virtual machine to be migrated based on historical accesslog of at least one application and memory log of the virtual machine tobe migrated, wherein predicting the migration memory size includes:computing a function relation between a memory size allocated by thevirtual machine to be migrated to the at least one application and arequest arrival rate of the at least one application within a period oftime based on a change in request arrival rate of the at least oneapplication and a change in memory size allocated by the virtual machineto be migrated to the at least one application within the period oftime; and predicting migration memory size required by the virtualmachine to be migrated based on the function relation; computingavailable migration bandwidth of a host of the virtual machine to bemigrated; computing virtual machine migration time based on thepredicted migration memory size required by the virtual machine to bemigrated and the available migration bandwidth of the host; settingretransmission time of the application client based on the virtualmachine migration time that was computed based on both the predictedmigration memory size required by the virtual machine to be migrated andthe available migration bandwidth of the host; and generating andtransmitting a time instruction to the application client based on theset retransmission time, wherein the application client is configured tosend a request to the virtual machine in accordance with the timeinstruction after the virtual machine has been migrated.
 2. The methodof claim 1, wherein the predicting migration memory size required by thevirtual machine to be migrated based on the function relation comprises:predicting migration memory size required by the at least oneapplication based on the function relation and request arrival rate ofthe at least one application at migration time; obtaining migrationmemory size required by the virtual machine to be migrated byaccumulating memory size required by the at least one application. 3.The method of claim 1, wherein the computing available migrationbandwidth of a host of the virtual machine to be migrated comprises: incase that there are a plurality of virtual machines requesting bandwidthfrom the host, if bandwidth of the host is greater than or equal tobandwidth requested by the plurality of virtual machines, then availablemigration bandwidth of the host of the virtual machine to be migrated is${W_{A} = {W_{S} - {\sum\limits_{i = 1}^{j}\; W_{i}}}},$ wherein W_(s)is bandwidth of the host, W_(i), (i=1 . . . j, j≥1) is bandwidthrequested by other virtual machines except the virtual machine to bemigrated.
 4. The method of claim 1, wherein the computing availablemigration bandwidth of a host of the virtual machine to be migratedcomprises: in case that there are a plurality of virtual machinesrequesting bandwidth from the host, if bandwidth of the host is smallerthan bandwidth requested by the plurality of virtual machines, thencomputing available migration bandwidth of the host of the virtualmachine to be migrated based on weight of the virtual machine to bemigrated.
 5. The method of claim 1, wherein the setting retransmissiontime of the application client based on the virtual machine migrationtime comprises: setting retransmission time of the application client tobe larger than migration time of the virtual machine.
 6. An apparatusfor setting retransmission time of an application client during virtualmachine migration, comprising: a migration memory predicting moduleconfigured to predict migration memory size required by a virtualmachine to be migrated based on historical access log of at least oneapplication and memory log of the virtual machine to be migrated,wherein the migration memory predicting module is further configured to:compute a function relation between a memory size allocated by thevirtual machine to be migrated to the at least one application and arequest arrival rate of the at least one application within a period oftime based on a change in request arrival rate of the at least oneapplication and a change in memory size allocated by the virtual machineto be migrated to the at least one application within the period oftime; and predict migration memory size required by the virtual machineto be migrated based on the function relation; an available bandwidthcomputing module configured to compute available migration bandwidth ofa host of the virtual machine to be migrated; a migration time computingmodule configured to compute virtual machine migration time based on thepredicted migration memory size required by the virtual machine to bemigrated and the available migration bandwidth of the host; and aretransmission time setting module configured to set retransmission timeof the application client based on the virtual machine migration timethat is computed by the migration time computing module based on boththe predicted migration memory size required by the virtual machine tobe migrated and the available migration bandwidth of the host, whereinthe retransmission time setting module is further configured to generateand transmit a time instruction to the application client based on theset retransmission time, wherein the application client is configured tosend a request to the virtual machine in accordance with the timeinstruction after the virtual machine has been migrated.
 7. Theapparatus of claim 6, wherein the migration memory predicting module isfurther configured to: predict migration memory size required by the atleast one application based on the function relation and request arrivalrate of the at least one application at migration time; obtain migrationmemory size required by the virtual machine to be migrated byaccumulating memory size required by the at least one application. 8.The apparatus of claim 6, wherein the available bandwidth computingmodule is configured to: in case that there are a plurality of virtualmachines requesting bandwidth from the host, if bandwidth of the host isgreater than or equal to bandwidth requested by the plurality of virtualmachines, then available migration bandwidth of the host of the virtualmachine to be migrated is${W_{A} = {W_{S} - {\sum\limits_{i = 1}^{j}\; W_{i}}}},$ wherein W_(s)is bandwidth of the host, W_(i), (i=1 . . . j, j≥1) is bandwidthrequested by other virtual machines except the virtual machine to bemigrated.
 9. The apparatus of claim 6, wherein the available bandwidthcomputing module is configured to: in case that there are a plurality ofvirtual machines requesting bandwidth from the host, if bandwidth of thehost is smaller than bandwidth requested by the plurality of virtualmachines, then compute available migration bandwidth of the host of thevirtual machine to be migrated based on weight of the virtual machine tobe migrated.
 10. The apparatus of claim 6, wherein the retransmissiontime setting module is further configured to: set retransmission time ofthe application client to be larger than migration time of the virtualmachine.
 11. A non-transitory, computer readable storage medium havinginstructions stored thereon that, when executed by a computer, implementa method of setting retransmission time of an application client duringvirtual machine migration, the method comprising: predicting, with aprocessing device, migration memory size required by a virtual machineto be migrated based on historical access log of at least oneapplication and memory log of the virtual machine to be migrated,wherein predicting the migration memory size includes: computing afunction relation between a memory size allocated by the virtual machineto be migrated to the at least one application and a request arrivalrate of the at least one application within a period of time based on achange in request arrival rate of the at least one application and achange in memory size allocated by the virtual machine to be migrated tothe at least one application within the period of time; and predictingmigration memory size required by the virtual machine to be migratedbased on the function relation; computing available migration bandwidthof a host of the virtual machine to be migrated; computing virtualmachine migration time based on the predicted migration memory sizerequired by the virtual machine to be migrated and the availablemigration bandwidth of the host; setting retransmission time of theapplication client based on the virtual machine migration time that wascomputed based on both the predicted migration memory size required bythe virtual machine to be migrated and the available migration bandwidthof the host; and generating and transmitting a time instruction to theapplication client based on the set retransmission time, wherein theapplication client is configured to send a request to the virtualmachine in accordance with the time instruction after the virtualmachine has been migrated.
 12. The non-transitory, computer readablestorage medium of claim 11, wherein the predicting migration memory sizerequired by the virtual machine to be migrated based on the functionrelation comprises: predicting migration memory size required by the atleast one application based on the function relation and request arrivalrate of the at least one application at migration time; obtainingmigration memory size required by the virtual machine to be migrated byaccumulating memory size required by the at least one application. 13.The non-transitory, computer readable storage medium of claim 11,wherein the computing available migration bandwidth of a host of thevirtual machine to be migrated comprises: in case that there are aplurality of virtual machines requesting bandwidth from the host, ifbandwidth of the host is greater than or equal to bandwidth requested bythe plurality of virtual machines, then available migration bandwidth ofthe host of the virtual machine to be migrated is${W_{A} = {W_{S} - {\sum\limits_{i = 1}^{j}\; W_{i}}}},$ wherein W_(s)is bandwidth of the host, W_(i), (i=1 . . . j, j≥1) is bandwidthrequested by other virtual machines except the virtual machine to bemigrated.
 14. The non-transitory, computer readable storage medium ofclaim 11, wherein the computing available migration bandwidth of a hostof the virtual machine to be migrated comprises: in case that there area plurality of virtual machines requesting bandwidth from the host, ifbandwidth of the host is smaller than bandwidth requested by theplurality of virtual machines, then computing available migrationbandwidth of the host of the virtual machine to be migrated based onweight of the virtual machine to be migrated.
 15. The non-transitory,computer readable storage medium of claim 11, wherein the settingretransmission time of the application client based on the virtualmachine migration time comprises: setting retransmission time of theapplication client to be larger than migration time of the virtualmachine.